A transparent material is a material through which visible light passes. A transparent material has a unique benefit that you can see through the material. A material cannot acquire transparency a posteriori by coloring. An a priori transparent material has been studied and developed in various industrial and artistic fields.
Since a transparent material can be applied in a wide range of uses, the transparent material has been required to have any of various properties as well as an opaque material. The conventional transparent or semi-transparent materials however fail to meet a requirement for strength or toughness on an article such as shoes and tires in practice.
In addition, a so-called transparent material may actually have various transparency. In the case that a material is muddy or hazy, the material would be unsuitable for preparing a transparent and aesthetic material.
Japanese laid-open patent application No. 2003-301080 discloses a transparent crosslinked rubber composition comprising ethylene/alpha-olefin/non-conjugated polyene copolymer rubber, ethylene/polar monomer copolymer, and silica.
Adding silica for strength of a material, however, has been known to impair the transparency of the material. A silica-containing material is sometimes called as transparent material, but indeed the material is clouded or yellowed. In addition, a silica-containing material requires a complicated process to disperse silica in order to improve its transparency.
A silicon-based material such as silicone resin and silica-containing resin generally needs oil as a softener to have flexibility. The more flexibility a silicon-based material has, the more oil is needed. Oil in a silicon-based material however leads to a “bleeding” over time, and its use has been actually restricted.
Japanese laid-open patent application No. 2005-002225 discloses a transparent composition comprising a rubber polymer containing two components having different refractive indices, and wet silica. Indeed the composition has an insufficient transparency, and cannot overcome the defects of conventional art. The prior composition also has the defects of silica.
Japanese laid-open patent application Nos. 2002-327092, 2002-363344 and 2003-041060 disclose crosslinked polybutadiene compositions. The conventional compositions are mere good in coloration, and cannot contribute to transparency.
Even though there has been many prior studies and demands in the field, the skilled artisan has not developed yet a composition having both high transparency and rubber properties such as hardness and strength. The fact is evidence of great difficulties to achieve the combination of the properties at higher level in a good balance.
In addition, if a conventional composition seems to have some transparency, it is often weak to heat. Such a material will deteriorate and lose its transparency by heating, and cannot be actually used in an article which is put under a severe condition (e.g., outdoor use or sterilization).
In general terms, it has been known in the art since earlier times that a catalyst including some alkali metals, alkali earth metals and transition metals may be used in some reactions for preparing olefins. But specific studies are still developing now in the art to verify which metal is actually suitable to be included in a catalyst to prepare which olefin.
Polyisoprene rubber (i.e., a polymer of 2-methyl-1,3-butadiene) is one of polyolefins. In the art it may be simply referred as “isoprene (component)” or “IR (component)”. Most of conventional polyisoprene rubbers have cloudy or hazy appearances in practice—even though some suppliers advertize that they are “transparent”. The conventional polyisoprenes are also generally weak to heat.
The conventional polyisoprene rubbers have been manufactured by using some conventional Ziegler-Natta catalysts or conventional catalysts including some alkaline metals or alkali earth metals such as calcium. The conventional metal-containing catalysts, however, often lead to an issue that the final composition contains some metal residues. Since articles that are configured to touch to human body are generally controlled by strict regulations, you cannot easily use the conventional metal-containing catalysts to meet the needs of the market.
Neodymium is one of rare earth metals and the 60th element of the Periodic Table, and belongs to lanthanoid. Neodymium has been used as a raw material for magnets, superconductors, and misch metals, but has not well known in the art of catalyst for olefin synthesis.
In the art of olefin synthesis, there are some catalysts including neodymium catalyst for polybutadiene synthesis; but there is only a few reports regarding polyisoprene synthesis Europe Patent No. 2,650,313, U.S. Pat. Publ. No. 20050137338, Henk van de Weg, R&TS Note KRTS 108 2011, Lars Friebe et al., Advances in Polymer Science, Vol. 204, 2006, pp. 1-154 and Wei Gao et al., J. Am Chem. Soc., 2008, 130 (14), pp. 4984-4991). In the few conventional studies, neodymium is not specifically stressed and is merely bundled with other transition metals. There is no prior study to particularly focus on any unique nature of neodymium for polyisoprene synthesis.